According to the inventors, memories currently used are as follows:
The most common memory is an SRAM with memory cells using 6 transistors. This memory is widely used as a single memory or an on-chip cache for a processor and the like, because it can be fabricated with a general transistor fabrication process.
Another common memory is a DRAM with memory cells composed of one transistor and one capacitor. This memory is also widely used for the main memory of personal computers due to its large capacity memory, because a DRAM is more highly integrated than a SRAM, although there is a problem to require a capacitor fabrication process.